Skill progression cannot be measured directly using hider (or seeker) reward, since the reward fluctuates heavily through skill progression (Figure REF , left). Instead, emergent skills can be mapped to behavioral shifts in the way agents interact with the tools in their environment [1]}. Ramp use by seekers (phase 3) can be detected by an increase in the average displacement of the ramp (Figure REF , middle), because seekers need to drag the ramp to wherever hiders have barricaded themselves. Ramp defense by hiders (phase 4) can be detected by an increase in the average ramp displacement during preparation time, because hiders need to drag the ramp out of the reach of seekers as long as seekers are immobilized (Figure REF , left).
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